1. Field of the Invention
The present invention relates to particulate construct such as microcapsules featured in that a solid phase containing polyhydroxyalkanoate (which may hereinafter be abbreviated as PHA) which at least contains 3-hydroxyalkanoic acid as a monomer unit incorporates at least one of solid phase, liquid phase and gaseous phase, and particulate construct such as microcapsules featured in that the aforementioned PHA coats at least one of solid phase, liquid phase and gaseous phase. The present invention also relates to a method for producing particulate construct such as microcapsuleas featured by causing, from w/o type emulsion consisting of water phase and oil phase containing at least PHA or w/o/w type emulsion obtained by emulsifying such w/o type emulsion in water phase, PHA to incorporate or coat at least one of solid phase, liquid phase and gaseous phase, for example a method for producing particulate construct such as microcapsules by in-liquid drying, phase separation, spray drying or a similar method.
The present invention further relates to a producing method of executing encapsulation with PHA from o/w type emulsion consisting of oil phase containing at least PHA and water phase, wherein such encapsulation is coating, for example a method for producing particulate construct such as microcapsules by in-liquid drying, phase separation, spray drying or a similar method.
The present invention further relates to a method for producing particulate construct such as microcapsules featured, in w/o type emulsion consisting of water phase and oil phase containing at least PHA or w/o/w type emulsion obtained by emulsifying such w/o type emulsion in water phase, by synthesizing PHA utilizing PHA synthesizing enzyme and 3-hydroxyacyl coenzyme A contained in the water phase thereby causing PHA to incorporate or coat at least one of solid phase, liquid phase and gaseous phase, wherein the encapsulation is coating.
The present invention further relates to a method for producing particulate construct such as microcapsules featured, in w/o type emulsion consisting of oil phase and water phase containing at least PHA synthesizing enzyme and 3-hydroxyacyl coenzyme A, by polymerizing 3-hydroxyacyl coenzyme A by the PHA synthesizing enzyme in the water phase to synthesize PHA thereby executing encapsulation with PHA, wherein the encapsulation is coating.
The present invention further relates to particulate construct such as slow-releasing microcapsules containing a chemical substance such as pharmaceuticals or agricultural chemicals, and a method for producing the particulate construct such as the above-mentioned microcapsules.
The present invention further relates to particulate construct containing pigment, dye, hemoglobin, cosmetic component or fertilizer component, and a producing method thereof. It further relates to an ink composition, a blood cell composition, a cosmetic composition or a fertilizer composition containing such particulate construct, and a producing method thereof.
The present invention further relates to hollow particulate construct such as hollow microcapsules incorporating gaseous phase, a producing method thereof, and an ultrasonic contrast medium utilizing such hollow particulate construct as an ultrasonic reflecting member. In addition, the present invention relates to the application of the hollow particulate construct such as the above-mentioned hollow microcapsules to the ultrasonic contrast medium administered orally or non-orally into a living organism and utilized for ultrasonic diagnosis.
2. Related Background Art
Microcapsules have been studied in various fields such as pharmaceuticals, agricultural chemicals, foods, adhesives and liquid crystals. For example, in the pharmaceutical field, application as a slow-releasing preparation has been studied to improve drugs of a short action period for prolonged action period, where not only prolonged pharmacological effects but also other effects such as decrease in the dosage, adverse effects, and improvement in the non-compliance are expected. Recently, various controlled release pharmaceutical preparations have been proposed that can release chemicals at a constant rate, substantially at zero-order. Such controlled release preparations are being developed as preparations for oral administration, injection, and skin patch application.
Microcapsules are also studied in various other fields, for example, in the cosmetic field, as means for delivering an unstable effective component to the desired site and releasing it slowly; in the agricultural field, as chemicals and fertilizers having slow-releasing function; and in the field of recording materials, as encapsulated inks.
In the pharmaceutical field, U.S. Pat. No. 6,146,665 discloses a method of producing fine porous particles of polyhydroxyalkanoate entrapping a hydrophilic drug therein, and a pharmaceutical composition comprising a core material being an oil drop dissolving therein a lipophilic drug encapsulated by a polyhydroxyalkanoate shell.
Although oral preparations have been widely investigated and developed and many preparations have been commercialized, injection preparations are limited to the depot preparations of insulin. This is ascribable to the lack of development of the polymer compound for conferring slow releasing function. In case of oral preparations, the polymer compound need not be decomposed in the body, but, in case of injection preparations, the polymer compound is absolutely required to be decomposed in, metabolized in and excreted from the body without expressing toxicity therein, and also required are other strict conditions such as absence of local disturbance in the injection site.
Under such circumstances, recently investigated are various polymer compounds, especially polylactic acid, lactic acid-glycolic acid copolymer and hydroxybutyric acid-glycolic acid copolymer, those employed as sewing thread in surgical operation, are expected as safe and useful polymer compounds (Japanese Patent Publication No. 1-57087, WO 94/10982 and Japanese Patent Applications Laid-open Nos. 8-151322 and 8-217691).
In fact, there have been reported various micro encapsulation techniques to prepare slow release preparations entrapping a hydrophilic drug in these polymer compounds. Also for poly-3-hydroxybutyric acid (which may hereinafter be abbreviated as PHB), there are reported microcapsules for controlled release of the active peptide component, and microcapsules containing lactide (Japanese Patent Application Laid-open No. 61-431119, Drug Delivery System 7(5), 367-371, 1992 and ibid., 8(2), 131-136, 1993). Also for 3-hydroxybutyric acid/4-hydroxybutyric acid copolymer, there is disclosed a slow release preparation capable of controlling the release rate of a physiologically active substance with the monomer ratio (Japanese Patent Application Laid-open No. 11-199514).
Most of these technologies are to include water-soluble drugs. For example, Japanese Patent Application Laid-open Nos. 60-100516 and 62-201816 disclose a method of producing highly dispersible slow release microcapsules of a water-soluble drug by using the in-water drying method at a high trapping rate. Also Japanese Patent Application Laid-open Nos. 1-163135 and 2-124814 disclose a method of including a water-soluble drug in a prophylactic acid-glycolic acid copolymer, and Japanese Patent Application Laid-open Nos. 2-124814 and 5-294839 disclose slow release preparations including a physiologically active polypeptide and cisplatin respectively. Also Japanese Patent Application Laid-open No. 4-321622 discloses long-term slow releasing microcapsules including copolymer or homopolymer of which lactic acid/glycolic acid ratio is 80/20 to 100/0 and weight-averaged molecular weight is 7,000 to 30,000, capable of releasing polypeptides at zero-order over two months or more.
The conventional production methods for the microcapsules can be largely classified into chemical methods such as interfacial polymerization and in-situ polymerization, physicochemical methods such as phase separation (coacervation), interfacial precipitation, in-liquid drying and orifice method, and mechanical methods such as spray drying and dry mixing. Among these methods, the interfacial polymerization, in-situ polymerization, in-liquid drying, orifice method and phase separation (coacervation) have been applied for microencapsulating water-soluble agents.
Although many reports have been made on the slow-releasing microcapsules containing various physiologically active polypeptides or water-soluble low molecular weight drugs (Critical Reviews in Therapeutic Drug Carrier Systems, 12, pp 1-9 (1995); Japanese Patent Publication No. 2-503315; EPA 0586238; J. Pharm. Sci., 75, pp 750-755 (1986); and Japanese Patent Application Laid-open No. 57-118512), most of such microcapsules are unsatisfactory in view of long-term slow releasing properties according to the applications, since (1) the drug leakage to the external water phase is high during the production process resulting in low trapping rate, (2) the obtained microcapsules are generally porous and show a large initial release, or (3) the physiologically active substance is modified during the production process leading to insufficient bioavailability.
As regards improvement of the slow releasing properties of microcapsules, Japanese Patent Application Laid-open No.61-63613 discloses, in microcapsules utilizing polylactic acid as the base material, to uniformly dissolve an oil-soluble additive (medium chain fatty acid triglyceride, lower fatty acid triglyceride etc.), being soluble in an organic solvent and digestable in the living body, in a solution of polylactic acid in such an organic solvent, in order to prevent the decrease of the releasing speed of the active component in the polylactic acid-based microcapsules after a certain time from the administration. However it does not teach preparation of microcapsules using other base materials or an aqueous solution of the active component. Japanese Patent Application Laid-open No. 8-151321 discloses microcapsules containing a polymer and an amorphous, water-soluble physiologically active substance, being produced from an S/O/W type emulsion, but it does not teach at all a production method of microcapsules containing an aqueous solution of a drug as the internal water phase or a method utilizing a metal complex of a water-soluble physiologically active peptide. Also EP 0765660 discloses microcapsules containing an amorphous 2-piperazinone-1-acetic acid derivative and use of an s/o/w emulsion in the preparation thereof, but does not teach a production method of microcapsules using an aqueous solution of a drug as the internal water phase or a method utilizing a metal complex of water-soluble physiologically active peptide. In general, in preparation of microcapsules containing a water soluble physiologically active substance, w/o type is superior to s/o type where the drug is used in solid state, in consideration of uniform drug content and operability. Thus, w/o type is preferable in the industrial scale mass production.
A problem often pointed out in the drug release control using a slow releasing preparation is a phenomenon called initial burst phenomenon, drug release in a large amount at a time in the initial releasing stage after administration of the preparation to the subject. If such an initial burst occurs, the drug concentration in the blood may exceed the permissible upper limit, endangering the subject. Although initial burst can be prevent to a certain extent by selecting the kind of the drug compound and structure of the biodegradable polymer, there has not been found a basic solution for preventing initial burst yet. On the other hand, there is a requirement for including a drug compound at a concentration as high as possible in microcapsules, in order to achieve slow release of the drug compound over a long period or to formulate an expensive drug in a certain amount of preparation as small as possible for economic advantage.
However, by the conventionally known methods for producing microcapsules, percentage of drug compound trapped in the microcapsules (trapping rate) tends to be lowered. In case of a water-soluble drug, especially, a serious problem is that the drug tends to escape outside the membrane, resulting in a low trapping rate. On the other hand, microcapsules prepared by a method enabling a high trapping rate have a drawback that initial burst tends to occur in the drug release.
Meantime, in the ultrasonic diagnosis or inspection, it is proposed to administer microballoons, which are small polymer spheres, into the living body as an ultrasonic reflecting agent. Small bubbles dispersed in liquid, i.e., microbubbles, are conventionally known to be a very effective ultrasonic reflector for the ultrasonic diagnosis or inspection. However, such microbubbles will disappear in a short time, in several minutes at longest even when a stabilizing agent is added. For this reason, microbubbles have to be administered in the patient immediately after preparation, and are therefore difficult to use in the actual medical locations. In addition, in order to facilitate permeation through the blood vessel after the administration into the body, the size of the bubbles has to be within a range of about 1 to 10 μm. Most of the generated microbubbles are within a range of 40 to 50 μm, so that such microbubbles are not necessarily suitable for administration to the body for the purpose of ultrasonic diagnosis.
In order to solve these drawbacks of microbubbles, it has been proposed administration of microballoons, small polymer spheres, to the body (for example, Japanese Patent Application Laid-open No. 3-94774). However, microballoons prepared by the conventional method must be administered in a large amount in order to obtain a high contrast effect. Partcularly, for the cardiac muscle, there is no effective contrast medium that can provide the required high contrast effect. This is primarily because such balloons often do not have hollow structure inside and it is difficult to obtain uniform small particles containing bubbles inside. Besides, such microballoons when administered in a large amount may give an excessive burden to the body, thus having a safety problem to be solved.
Meanwhile, active studies have been done to produce polymer compounds by using biotechnology, and partly in practice. For example, known microbial polymers include polyhydroxyalkanoates (PHAs) such as poly-3-hydroxy-n-butyric acid (PHB), and copolymers of 3-hydroxy-n-butyric acid and 3-hydroxy-n-valeric acid (PHB/V); polysaccharides such as bacterial cellulose and pullulan; and polyamino acids such as poly-γ-glutamic acid and polylysine. Particularly, PHA can be processed into various products by melt-preparation etc., just like other existing plastics. In addition, because of excellent biocompatibility, application of PHA as medical soft materials is also expected.
It has beep reported that many microorganisms produce PHA and accumulate it within cells. For example, microbial productions of PHB/V by Alcaligenes eutrophus H16 (ATCC No. 17699), Methylbacterium sp., Paracoccus sp., Alcaligenes sp., and Pseudomonas sp. have been reported (for example, Japanese Patent Application Laid-Open No 5-7492, Japanese Patent Publication Nos. 6-15604, 7-14352, and 8-19227). Furthermore, Comamonas acidovorans IFO 13852 produces PHA comprised of monomer units of 3-hydroxy-n-butyric acid and 4-hydroxy-n-butyric acid (Japanese Patent Application Laid-Open No. 9-191893), and Aeromonas caviae produces a copolymer of 3-hydroxy-n-butyric acid and 3-hydroxyhexanoic acid (Japanese Patent Application Laid-Open Nos. 5-93049 and 7-265065).
Biosynthesis of these PHB and PHB/V is an enzymatic polymerization reaction using as a substrate (R)-3-hydroxybutyryl CoA or (R)-3-hydroxyvaleryl CoA that is synthesized from various carbon sources through various metabolic pathways within a living organism. The enzyme that catalyzes this polymerization reaction is PHB synthetase (this can be referred to as PHB polymerase or PHB synthase). CoA is an abbreviation for coenzyme A, and its chemical structure is represented by the following chemical formula.

Recently, active studies on polyhydroxyalkanoate comprised of 3-hydroxyalkanoic acid units of medium-chain-length (about 3 to 12 carbon atoms) (mcl-PHA) have been conducted.
For example, Japanese Patent No. 2642937 discloses that Pseudomonas oleovorans ATCC 29347 can produce PHA comprised of 3-hydroxyalkanoic acid monomer units of 6 to 12 carbon atoms from non-cyclic aliphatic hydrocarbons. In addition, it has been reported, in Appl. Environ. Microbiol., 58, 746 (1992), that Pseudomonas resinovorans produces PHA of which monomer units are 3-hydroxy-n-butyric acid, 3-hydroxyhexanoic acid, 3-hydroxyoctanoic acid, and 3-hydroxydecanoic acid using octanoic acid as a sole carbon source, and it also produces PHA of which monomer units are 3-hydroxy-n-butyric acid, 3-hydroxyhexanoic acid, 3-hydroxyoctanoic acid, and 3-hydroxydecanoic acid using hexanoic acid as sole carbon source. Here, the 3-hydroxyalkanoic acid monomer units longer than the raw material fatty acid are considered derived from the fatty acid synthesizing pathway described below.
Int. J. Biol. Macromol., 16 (3), 119 (1994) reported that Pseudomonas sp. Strain 61-3 produces PHA comprised of monomer units of 3-hydroxyalkanoic acids such as 3-hydroxy-n-butyric acid, 3-hydroxyhexanoic acid, 3-hydroxyoctanoic acid, and 3-hydroxydecanoic acid, and 3-hydroxyalkenoic acids such as 3-hydroxy-5-cis-decenoic acid and 3-hydroxy-5-cis-dodecenoic acid, using sodium gluconate as a sole carbon source.
The above-described PHAs are comprised of monomer units having alkyl groups as the side chain (usual-PHAs). However, when wider application of PHA, e.g., as a functional polymer, is intended, PHA having side chains other than alkyl groups (for example, side chains having substituents such as phenyl group, unsaturated hydrocarbons, ester groups, allyl group, cyano group, halogenated hydrocarbons, and epoxides) is extremely useful (unusual-PHA).
As for biosynthesis of unusual-PHA having phenyl groups, it was reported that Pseudomonas oleovorans produced PHA having 3-hydroxy-5-phenylvaleric acid units from 5-phenylvaleric acid (Macromolecules, 24, 5256-5260 (1991), Macromol. Chem., 191, 1957-1965 (1990); Chirality, 3, 492-494 (1991)). Polymers, 29, 1762-1766 (1996) reported that Pseudomonas oleovorans produced PHA having 3-hydroxy-5-(4-tolyl)valeric acid units from 5-(4-tolyl)valeric acid (5-(4-methylphenyl)valeric acid). Further, Polymers, 32, 2889-2895 (1999) reported that Pseudomonas oleovorans produced PHA having 3-hydroxy-5-(2,4-dinitrophenyl) valeric acid units and 3-hydroxy-5-(4-nitrophenyl)valeric acid units from 5-(2,4-dinitrophenyl)valeric acid.
As for unusual-PHA having phenoxy groups, Macrocol. Chem. Phys., 195, 1665-1672 (1994) reported that Pseudomonas oleovorans produced PHA having 3-hydroxy-5-phenoxyvaleric acid units and 3-hydroxy-9-phenoxynonanoic acid units from 11-phenoxyundecanoic acid. Also, Polymers, 29, 3432-3435 (1996) reported that Pseudomonas oleovorans produced a PHA having 3-hydroxy-4-phenoxybutyric acid units and 3-hydroxy-6-phenoxyhexanoic acid units from 6-phenoxyhexanoic acid, a PHA having 3-hydroxy-4-phenoxybutyric acid units, 3-hydroxy-6-phenoxyhexanoic acid units, and 3-hydroxy-8-phenoxyoctanoic acid units from 8-phenoxyoctanoic acid, and a PHA having 3-hydroxy-5-phenoxyvaleric acid unit and 3-hydroxy-7-phenoxyheptanoic acid units from 11-phenoxyundecanoic acid. Further, Can. J. Microbiol., 41, 27-34 (1995) reported that Psudomonas oleovorans ATCC 29347 and Pseudomonas putida KT 2442 produced PHA having 3-hydroxy-p-cyanophenoxyhexanoic acid units and PHA having 3-hydroxy-p-nitrophenoxyhexanoic acid units from p-cyanophenoxyhexanoic acid and p-nitrophenoxyhexanoic acid respectively. Japanese Patent No. 2989175 describes a homopolymer comprised of 3-hydroxy-5-(monofluorophenoxy)valeric acid units or 3-hydroxy-5-(difluorophenoxy)valeric acid units and a copolymer containing at least 3-hydroxy-5-(monofluorophenoxy)pentanoate unit or 3 -hydroxy-5-(difluorophenoxy)pentanoate unit and a method for producing such homopolymer or copolymer, reciting that such homopolymer and copolymer can provide water-repellency and stereoregularity with high melting point and good workability.
As an example of unusual-PHA having a cyclohexyl group, Polymers, 30, 1611-1615 (1997) reported that Pseudomonas oleovorans produced such PHA from cyclohexylbutyric acid or cyclohexylvaleric acid.
Among the PHAs having a substituent in the side chain, development of PHA having a sulfide (—S—) sulfur atom in the side chain was reported in Macromolecules, 32, 8315-8318(1999) utilizing Pseudomonas putida 27N01 strain and also utilizing octanoic acid and 11-(phenylsulfanyl) undecanoic acid as substrate to produce PHA containing 3-hydroxy-5-(phenylsulfanyl) valeric acid and 3-hydroxy-7-(phenylsulfanyl) heptanoic acid as monomer units. In this process there was employed a method of preculturing the Pseudomonas putida 27N01 strain in a culture medium containing only octanoic acid as the growth substrate, and inoculating the obtained seed culture in a culture medium containing only 11-(phenylsulfanyl) undecanoic acid as the substrate.
Also Polymer Preprints, Japan, Vol. 49, No. 5, 1034(2000) reported production utilizing Pseudomonas putida 27N01 strain and utilizing 11-[(phenylmethyl)sulfanyl] heptanoic acid as the substrate to produce PHA consisting of two monomer units, namely 3-hydroxy-5-benzylthio-valeric acid and 3-hydroxy-87-[(phenylmethyl)sulfanyl] heptanoic acid. In this process there was employed a method of preculturing the Pseudomonas putida 27N01 strain in a culture medium containing octanoic acid only as the proliferating substrate, and inoculating the obtained culture liquid in a culture medium containing 11-[(phenylmethyl)sulfanyl] undecanoic acid only as the substrate.
These mcl-PHA and unusual-PHA are synthesized through an enzymatic polymerization reaction using (R)-3-hydroxyacyl CoA as a substrate. Such 3-hydroxyacyl CoAs are produced through various metabolic pathways (for example, β-oxidation pathway or fatty acid synthesis pathway) in a living organism from different alkanoic acids. The enzyme that catalyzes this polymerization reaction is PHA synthetase (this can be referred to as PHA polymerase or PHA synthase). The following is the reaction route from alkanoic acid to PHA via the β-oxidation pathway and polymerization reaction by PHA synthetase.

On the other hand, when the production is performed through the fatty acid synthesis pathway, it is considered that (R)-3-hydroxyacyl-ACP (ACP means acyl carrier protein) generated in this pathway is converted to (R)-3-hydroxyacyl CoA from which PHA is synthesized by PHA synthetase.
Recently, attempts have been made to synthesize PHA in vitro using PHB synthetase or PHA synthetase isolated from cells.
For example, Proc. Natl. Acad. Sci. USA, 92, 6279-6283 (1995) describes that PHB comprised of 3-hydroxy-n-butyric acid units has been successfully synthesized by using PHB synthetase derived from Alcaligenes eutrophus and 3-hydroxybutyryl CoA as a substrate. In addition, Int. J. Biol. Macromol., 25, 55-60 (1999) describes that PHA comprised of 3-hydroxy-n-butyric acid units or 3-hydroxy-n-valeric acid units has been successfully synthesized by reacting PHB synthetase derived from Alcaligenes eutrophus with 3-hydroxybutyryl CoA or 3-hydroxyvaleryl CoA. Further, this report mentions that, when racemic 3-hydroxybutyryl CoA was reacted with PHB synthetase, PHB comprised of only (R) 3-hydroy-n-butyric acid units was successfully synthesized due to the stereoselectivity of the enzyme. Macromol. Rapid Commun., 21, 77-84 (2000) reported in vitro PHB synthesis using PHB synthetase derived from Alcaligenes eutrophus. 
FEMS Microbiol. Lett., 168, 319-324 (1998) describes that PHB comprised of 3-hydroxy-n-burytic acid units was successfully synthesized by reacting PHB synthetase derived from Chromatium vinosum with 3-hydroxybutyryl CoA.
In Appl. Mirobiol. Biotechnol., 54, 37-43 (2000), PHA comprised of 3-hydroxydecanoic acid is synthesized by reacting PHA synthetase derived from Pseudomonas aeruginosa with 3-hydroxydecanoyl CoA.
[Problems to Be Solved]
As described above, application of biotechnological methods to polymer synthesis may enable synthesis of new polymer compounds which can not be made by conventional organic synthesis or enable imparting new functions and constructs to polymer compounds. In addition, there are many cases where conventional multi-step reaction can be replaced with only one step reaction, so that simplification of the production process, cost reduction, and time saving are expected. Further, this enables consumption reduction of organic solvents, acids, alkalis, surfactants, etc., moderate reaction conditions, and synthesis from non-petroleum raw materials or crude raw materials, thus enables a synthesis process of lower environmental burden and of resource-recycling type. In more detail with synthesis from the crude raw materials, the substrate specificity of the enzyme used as a catalyst in biotechnological synthesis is high in general, so that it is possible to selectively promote a desired reaction even when the low purity raw material is used. Thus, use of waste materials or recycled materials can be expected.
Meantime, the present inventors were paying attention to microcapsules of a drug coated with a polymer compound as an elementary technology to confer a large additional value upon a polymer compound. By coating a drug with a polymer compound, the obtained microcapsules acquire very useful functionalities, particularly slow releasing ability. Conventionally, such microcapsules have been mostly prepared by organic synthesis.
If such microcapsules can be produced by a bioengineering method as explained above, it is expected to enable utilization of novel polymer compounds and realization of novel functions and structures, and also to realize a manufacturing process of low environmental burden and resource recycling with a low cost. For example, utilizing very strict molecular recognizing ability and stereo selectivity specific to the catalytic action of living organisms, there can be produced microcapsules covered with a novel functional polymer compound or a polymer compound of extremely high chirality by an extremely simple process of environmentally low burden.
Therefore, the object of the present invention is to provide particulate construct such as microcapsules utilizing the aforementioned highly functional polymer compound and a producing method therefor, and a method for producing particulate construct such as microcapsules by a bioengineering process.
As explained in the foregoing, the inclusion of a water-soluble drug in microcapsules comprised of polylactic acid or lactic acid-glycollic acid copolymer which are biodegradable polymers still has many issues in the drug releasing characteristics. Also the water-soluble drug has a drawback of tending to be easily dispersed and not effectively contained in the particulate construct or not microencapsulated.
The present invention is conceived to resolve the drawbacks of the aforementioned conventional technologies, and the object of the present invention is to provide a slow releasing preparation not showing practically defective initial release and showing practically acceptable zero-order release for a predetermined period even in case of particulate construct such as microcapsules including a drug, particularly a water-soluble drug, or microcapsules including a water-insoluble drug (including drugs generally called hardly soluble in water), and a producing method therefor. Also the present invention is to provide a slow releasing preparation of a high drug content stably including a drug, particularly a water-soluble drug, in particulate preparation such as microcapsules, and a producing method therefor.
For example, the fine particles disclosed in the U.S. Pat. No. 6,146,665 are those trapping a hydrophilic drug in porous granules consisting of polyhydroxyalkanoate free of toxicity, biodegradable and capable of in situ trapping the drug, but, because of porous structure, they rapidly release the hydrophilic drug by diffusion, so that the slow releasing property is difficult to control.
A problem to be resolved by the present invention is to optimize the drug holding ability and slow releasing ability by optimizing the structure of polyhydroxyalkanoate, thereby providing drug holding particles excellent in holding ability and capable of controlling the slow releasing ability even for hydrophilic drugs, other water-soluble substances, oleophilic drugs or other hydrophobic substances.
Further, the present invention provides particulate construct including a pigment, a dye, an agricultural chemical component, hemoglobin, a cosmetic component or a fertilizer component in the aforementioned particulate construct and a producing method therefor. It further provides an ink composition, an agricultural chemical composition, a hemocyte composition, a cosmetic composition or a fertilizer composition including such particulate construct, and a producing method therefor.
Also, as explained in the foregoing, the microballoons obtained in the conventional method, in which the particles do not have hollow structure inside and uniform fine particles including many bubbles are difficult to obtain, have to be administered in a large amount in order to obtain a high contrast effect in the ultrasonic diagnosis or inspection, and, particularly in contrast formation of the cardiac muscles, there has not been an effective contrast medium capable of sufficiently meeting the desired high contrast effect. The administration of such microballoons in a large amount may give an excessive burden to the living organism in certain cases and there are problems to be solved in terms of safety.
In consideration of the foregoing, the present invention is to provide a method for producing hollow particulate construct such as hollow microcapsules, capable of selectively obtaining fine particles having a hollow structure of microcapsule shape having a single PHA membrane in order to include many bubbles in the fine particles, and also provides an ultrasonic contrast medium exhibiting high contrast effect utilizing the hollow particulate constructe such as hollow microcapsules and a producing method therefor. More specifically, it provides an ultrasonic contrast medium of high contrast effect, usable for ultrasonic diagnosis or inspection of cardiac muscles, cardiac cavity and liver.